The invention relates generally to the field of pumps, and in particular, to improved mixed flow pumps for marine propulsion and hydraulic applications.
Conventional propulsors include numerous propeller, pumpjet and water jet propulsion devices. These devices are typically powered by an engine at a distance from the propulsor that is connected by a shaft to the propulsor. The engine is typically contained within a ship hull or pressure hull. Usually, a drive shaft extends from the engine through the pressure hull to the propeller, and bearings and a pressure seal are required to support the shaft and provide water-tight integrity for the engine and hull. These conventional propulsors contain motors that are located inside the pressure hull and that are directly coupled to a propeller that is located outside the pressure hull, with the flow being an external, rather than an internal flow.
Some examples of prior art patents include U.S. Pat. Nos. 6,273,768; 6,267,632; 6,203,388; 6,168,485; and 3,939,794. For example, U.S. Pat. No. 6,273,768 teaches that it is known to propel a boat or other watercraft using a water jet apparatus mounted to the hull, with the powerhead being placed inside (inboard) or outside (outboard) the hull. The drive shaft of the water jet apparatus is coupled to the output shaft of the motor. The impeller is mounted on the drive shaft and installed in a housing, the interior surface of which defines a water tunnel having a convergent nozzle. The impeller is designed such that during motor operation, the rotating impeller impels water rearward through the water tunnel and out the convergent nozzle. The reaction force propels the boat forward.
Conventional pumps include radial, axial, and mixed flow pumps. In a typical axial flow pump, the radial distance of a fluid particle from the pump centerline is constant from the pump inlet to the pump outlet. In radial and mixed flow pumps, the radial distance of a fluid particle from the pump centerline increases along the length of the pump because these types of pumps typically include a scroll or spiral type casing. Mixed flow pumps typically have a discharge that is perpendicular to the axis of impeller rotation.
A problem with conventional propulsors is that they typically do not include any flow conditioning of the fluid flow entering the pump impeller. For example, it may be desirable to condition the inlet flow to affect pump performance in some way, such as to reduce cavitation and improve acoustic performance of the propulsor, increase the head rise potential of the pump, and the like. Cavitation is generally undesired in conventional pumping systems because cavitation results in lost thrust and acoustic noise.
For example, U.S. Pat. No. 5,947,680 discloses turbomachinery with variable angle inlet guide vanes and variable angle diffuser vanes. However, the turbomachinery disclosed in U.S. Pat. No. 5,947,680 only teaches straight inlet guide vanes that are controlled in conjunction with the diffuser vanes to control the angle of the vanes to suit an operating condition. Also, the turbomachinery disclosed in U.S. Pat. No. 5,947,680 has variable geometry vanes, not fixed geometry guide vanes. This design is to adjust the performance to an optimum over a range of operating points and does not, for example, provide superior performance at one operating point. The device disclosed in U.S. Pat. No. 5,947,680 also includes a scroll discharge casing.
Another problem is flow conditioning of the outlet flow exiting the pump impeller. For example, in radial and mixed flow pumps, the rotating impeller imparts swirl to the flow as the impeller rotates and this swirl velocity decreases the pump performance.
Conventional propulsion pumps include various means for straightening the fluid flow exiting the impeller. For example, U.S. Pat. No. 4,427,338 discloses thrust control vanes for waterjets. The flow straightening vanes of the waterjets pump are designed to produce a low-pressure area, and the downstream side of the rotor drum is located inside the low-pressure area to eliminate the need for an axial thrust control seal. Also, U.S. Patent No. 4,929,200 discloses fixed flow-correction guide vanes positioned downstream of a rotating impeller. A number of gas injection slots are situated in the area of the trailing edges of the vanes for introducing a volume of gas into the flow in the tail pipe section of the pump in order to reduce internal drag resulting from pressure exercised by the water against the pump casing. U.S. Pat. No. 6,102,757 discloses a water jet propulsion device for a marine vessel having guide vanes provided in the water passage in the rear of the impeller for converting the guided swirl flows exiting the impeller into straight flows. U.S. Pat. No. 5,417,547 discloses a vaned diffuser for centrifugal and mixed flow pumps having two rows of radially displaced vanes to more efficiently convert the kinetic energy of the fluid flowing out from the impeller into static pressure. In addition, U.S. Pat. No. 5,480,330 discloses using a second impeller located rearward of a first impeller and which serve to straighten the rearwardly directed water flow.
Therefore, a need exists for a mixed flow pump having improved pump performance, reduced cavitation, and improved acoustics performance. The need also exists for a co-axial mixed flow pump.
The present invention is directed to a co-axial mixed flow pump system having one or more of improved pump performance, reduced caviatation, and reduced acoustic noise. The mixed flow pump includes an outer casing having a longitudinal centerline axis and a central body aligned co-axially within the outer casing along the longitudinal centerline axis. An axial forward looking inlet is formed along the longitudinal centerline axis for receiving a flow of fluid. A mixed flow pump having an impeller rotatably mounted to a forward end of the central body. The mixed flow impeller includes a hub, a plurality of blades extending outward from the hub, and a plurality of flow passages formed between adjacent blades. The mixed flow pump impeller rotates about the longitudinal centerline axis to draw a flow of fluid into the mixed flow impeller through the inlet and imparts energy to the fluid flow. An annular passageway is formed between the outer casing and the central body on a downstream side of the mixed flow pump impeller for receiving the fluid flow exiting the mixed flow impeller. The annular passageway is aligned axially. A plurality of stator vanes are disposed between and connecting the outer casing and the central body to condition the flow exiting the mixed flow impeller to flow generally in the axial direction. The mixed flow pump system also includes an axial rearward looking outlet formed along the longitudinal centerline axis for discharging the flow of fluid from the mixed flow pump system.
According to one aspect of the invention, the mixed flow pump, further includes an inlet section extending forward of the axial forward looking inlet. The inlet section has a distal inlet opening at a forward end and a length of inlet ducting connecting the inlet opening to the mixed flow pump impeller. In an alternate embodiment, the inlet section can further include a flush type inlet upstream of the axially aligned inlet to the mixed flow pump.
According to another aspect of the invention, the mixed flow pump can further include a plurality of inlet flow conditioning vanes disposed in the inlet section to condition a fluid flow flowing into the mixed flow pump impeller. The inlet flow conditioning vanes can be connected at a first end to the inlet ducting and extending into the inlet ducting to a distal end. The inlet flow conditioning vanes can comprise straight vanes attached to and extending radially inward from the outer casing into the fluid flow to eliminate any distortions in the fluid flow.
According to another aspect of the invention, the inlet flow conditioning vanes can comprise curved vanes that are curved in the same direction as the direction of impeller rotation to impart swirl to the fluid flow entering the mixed flow pump impeller to reduce the relative velocity of the fluid flow in order to decrease cavitation and vibration noise. In an alternative embodiment, the inlet flow conditioning vanes can comprise curved vanes that are curved into a direction of impeller rotation to impart swirl to the fluid flow entering the impeller and to increase the relative velocity of the fluid flow entering the mixed flow pump impeller to increase the mixed flow pump head rise potential.
In accordance with another aspect of the invention, the inflow conditioning vanes extend radially into the inlet duct from the outer casing in a radial direction toward the centerline axis of the outer casing. Alternatively, the inlet flow conditioning vanes can be leaned in a circumferential direction as the inlet flow conditioning vanes extend into the inlet duct.
Furthermore, the mixed flow pump can further include a center member extending axially forward from the central body into the inlet section. In embodiments having a center member, the inlet flow conditioning vanes can extend radially and be connected between the center member and the outer casing.
In accordance with another aspect of the invention, fluid flow enters the mixed flow pump impeller axially, flows through the mixed flow pump impeller at an angle from the longitudinal centerline axis such that a pressure developed by the mixed flow pump impeller is developed partly by centrifugal force and partly by a lift of the impeller blades on the fluid, and discharges the mixed flow pump impeller axially.
According to another aspect of the invention, the mixed flow pump impeller blades can include an open blade construction having a clearance gap formed between a distal end of the impeller blades and the outer casing blades. In an alternate embodiment, the mixed flow pump impeller blades can include a shrouded blade construction having a shroud disposed at a distal end of each of the impeller blades. In yet another embodiment, the impeller blades can include an embedded shrouded blade construction, wherein the shrouds of the shrouded impeller blades extend into and rotate within a groove in the outer casing.
Furthermore, the mixed flow pump can include a drive motor that is mounted axially rearward of the mixed flow impeller in the fluid flow. The motor can be housed the central body. Alternatively, the motor can be mounted outside of the fluid flow and a drive shaft, gears, bearings, etc. can connect the motor to the pump impeller. In addition, a rim-drive type motor may be used to drive the mixed flow pump impeller.
The plurality of stator vanes supporting the central body within the outer casing can include a curved wing-like shape for helping to remove swirl velocity from the fluid flow exiting the mixed flow impeller and straightening the fluid flow to flow generally in the axial direction. Preferably, the stator vanes are positioned at equal spacing around a circumference of the central body.
Moreover, the mixed flow pump can include one or more fairings to help facilitate a smooth flow of fluid though the outer casing and around the central body. For example, an inlet fairing can be provided that extends forward from a front end of the central body toward the inlet section and provides smooth flow into the impeller section and around the central body. An outlet fairing can be provided that extends rearward from a rear end of the central body toward the outlet section in order to facilitate a smooth flow as the flow exits the annular passageway.
In accordance with another aspect of the invention, the mixed flow pump can further include an outlet section having a forward end proximate the axial rearward looking outlet and a length of outlet ducting connecting the annular passageway to a discharge nozzle. The discharge nozzle can be positioned in the outlet ducting proximal a discharge opening for accelerating the fluid flow as the fluid flow is discharged from the mixed flow pump.
In accordance with another embodiment within the scope of the present invention, a mixed flow pump is provided for inputting hydraulic energy to a fluid flowing therethrough. The mixed flow pump includes an outer casing aligned axially from a forward end to a rearward end. The outer casing includes an inlet section, an impeller section, and an outlet section.
The inlet section includes an axially aligned inlet opening at the forward end and an axially aligned inlet duct having a generally increasing cross-sectional area from a first end of the inlet duct proximal the inlet opening to a second end of the inlet duct.
The impeller section is connected to a downstream end of the inlet section. The impeller section includes an axially aligned impeller inlet connected to the second end of the inlet section. An impeller sweep area having a generally increasing circular cross-sectional area is defined between the impeller inlet and an impeller outlet.
The outlet section is connected to a downstream end of the impeller section. The outlet section includes an axially aligned inlet at a forward end of the outlet section connected to the impeller outlet and an axially aligned outlet duct having a generally decreasing cross-sectional area from the outlet section inlet to a discharge opening.
According to another aspect of the invention, a central body can be disposed within and co-axial with the outer casing. The central body includes a stationary hub disposed within the outlet section, a mixed flow pump impeller rotatably mounted to a forward end of the hub and in the impeller section for drawing a flow of fluid through the inlet duct and into the mixed flow pump impeller. An annular passageway is formed between the central body and the outer casing and in the outlet section. A stator blade assembly is disposed between and connects the central body and the outer casing to provide structural support for the central body, to remove any swirl velocity from the fluid flow exiting the mixed flow pump impeller, and to convert kinetic energy contained within the swirl velocity to pressure.
A drive motor is provided for driving the impeller hub, causing the impeller to rotate thereby adding hydraulic energy to the fluid flowing through the mixed flow pump.
Inlet flow conditioning vanes can be disposed in the inlet section to condition a flow of fluid into the mixed flow pump impeller. The inlet flow conditioning vanes can include curved vanes having a wing shape, wherein the curved vanes are oriented to curve or turn in the same direction as the direction of rotation of the mixed flow pump impeller, thereby reducing the relative velocity of the fluid flow entering the mixed flow pump and reducing cavitation, or the inlet flow conditioning vanes can curve or turn into the direction of rotation of the mixed flow pump impeller, thereby increasing the relative velocity of the fluid flow entering the mixed flow pump and increasing the head rise potential of the mixed flow pump.
The inlet flow conditioning vanes can extend radially into the inlet duct from the outer casing toward the longitudinal centerline. Alternatively, the inlet flow conditioning vanes can be leaned in a circumferential direction as they extend into the inlet duct.
In accordance with another embodiment of the present invention, a co-axial propulsion system for use in propulsion and hydraulic applications can be provided. The coaxial propulsion system includes an outer casing for containing and guiding a fluid flow within the co-axial propulsion system. The outer casing includes ducting having a longitudinal centerline. The outer casing has a forward looking, axial inlet opening centered about the longitudinal centerline for receiving an axial flow of fluid from one of an internal fluid system and an exterior fluid operating environment into an interior of the co-axial propulsion system. The outer casing also has a rearward looking, axial outlet opening centered about the longitudinal centerline for discharging an axial flow of fluid from the interior of the co-axial propulsion system to one of the internal fluid system and the exterior fluid operating environment. The ducting extends axially and connects the inlet opening and the outlet opening.
A central body is disposed co-axially within the outer casing, A mixed flow pump impeller is rotatably mounted to the central body and disposed co-axially about the longitudinal centerline, wherein an axis of rotation of the mixed flow pump impeller is co-axial with the longitudinal centerline of the outer casing. An annular passageway defined between the outer casing and the central body, the annular passageway being oriented co-axially about the longitudinal centerline.
A plurality of stator vanes are disposed co-axially the the longitudinal centerline and extend radially between the outer casing and the central body and also extend through the annular passageway. The stator vanes support the central body within the outer casing. The stator vanes are configured to remove swirl velocity from the fluid flow exiting the mixed flow impeller and straightening the fluid flow to flow in an axial direction toward the outlet opening.
In accordance with another aspect of the invention, the ducting further includes inlet ducting formed between the inlet opening and the impeller section and a plurality of inlet flow conditioning vanes disposed in the inlet ducting for conditioning a fluid flow to improve one or more of cavitation performance and acoustic performance of the co-axial propulsion system.
In accordance with another aspect of the invention, the ducting further includes outlet ducting and a discharge nozzle for discharging the fluid flow from the ducting to produce thrust, wherein the outlet ducting is formed between the impeller section and the outlet opening and wherein the plurality of stator vanes are disposed in the outlet ducting.
In a further embodiment of the invention a co-axial mixed flow pump system is provided for propulsion and hydraulic applications. The co-axial mixed flow pump system includes an outer casing axially aligned about a centerline axis, a central body disposed within the outer casing and aligned about the centerline axis. A mixed flow pump is rotatably mounted to a front end of the central body and has an axis of rotation that is coincident with the centerline axis. A plurality of stator vanes are disposed between and connect the outer casing and the central body for removing swirl velocity from a flow exiting the mixed flow pump and causing the exiting flow to flow in an axial direction.
The co-axial mixed flow pump system also includes an internal flow passage defined by the outer casing. The internal flow passage further includes an axially inlet flow passage, an axial inlet to the mixed flow pump, an axial discharge from the mixed flow pump, an axially aligned annular flow passage defined between the outer casing and the central body, and an axially aligned outlet flow passage.
Additional features of the present invention are set forth below.